She’d call up the director, David Leitch, with her extreme doubts after she spent her first two weeks of training only fine-tuning a fight stance. “I said, ‘This is never going to work!’ I look like Big Bird,” Theron recalled. “I’m cupping small t–ties, and I don’t know what I’m doing.”

But she got the hang of it, thanks to her team of eight trainers and months of gym time. “Atomic Blonde” is a throwback of sorts — an action thriller set in 1989 Berlin that would make James Bond proud, with shades of “Alias” meets “The Bourne Identity.” Judging from the hoots and applause at SXSW — usually a reliable barometer of box office success — the movie is poised to be a massive summer hit for Focus Features when it opens on July 28.

Theron spent five years developing the project, based on the British graphic novel “The Coldest City.” Her character is the kind usually portrayed onscreen by men — or Angelina Jolie. Theron eventually learned how to do many of her own stunts. “I was like, ‘We’re going to pretend that, right?’” Theron said she asked her director. “David was like, ‘No, you’re actually going to throw big dudes.’ All right, let’s throw some big dudes.”

She’d run into Keanu Reeves, who was training at the same gym for “John Wick 2.” “We would spar with each other and s–t like that,” Theron added. (When a member of the audience asked if there could be a crossover movie, Leitch, who directed both, responded gamely: “‘Atomic Wick’? Yes.”)

There were some hazards to this line of work. “My teeth are in bad shape,” Theron said. “I’m actually still undergoing surgery. It’s really crazy. When I trained, I cracked two teeth in the back of my mouth, clenching while fighting, because apparently my arm strength wasn’t strong enough.” She had to complete an operation before the shoot started. “And I’m still f—ing dealing with it,” she sighed.